This invention relates to a synchronization control system for plural-shaft servo motors and, more particularly, to a synchronization control system capable of changing synchronization conditions as desired even during driving.
Among industrial machines incorporating a servo control system such as a robot, there is one which controls an operation of an object of control by a cooperative movement of plural shafts. For example, a double-shaft servo control is employed for moving a single object of control (e.g., an arm of a robot) two-dimensionally and a triple-shaft servo control is employed for moving it three-dimentionally. For winding an article unwound from a supply roll on a take-up roll, a double shaft servo control is made with the take-up roll and the supply roll. There are also numerous other examples among control systems of industry machines or other machines which perform a servo control of plural shafts synchronously or asynchronously.
In prior art synchronization control systems for plural-shaft servo motors, desired contents for control parameters of the following items are programmed beforehand by manual inputting or teaching, and driving of the servo motor is effected on the basis of this program:
(1) Combination of servo motor shafts which become an object of a synchronized driving.
(2) Type of interpolation defining a locus of the object of control from one set position to a next set position (e.g., linear interpolation or arc interpolation).
(3) Acceleration or deceleration time of the object of control moved by the synchronization control of plural shafts (i.e., acceleration or deceleration time relating to a resultant composite vector of plural shafts which are synchronously controlled).
(4) Moving speed at a constant speed of the object of control moved by the synchronization control of plural shafts (i.e., moving speed at a constant speed of a resultant composite vector of plural shafts which are synchronously controlled).
In the above described synchronization control system according to the program, the start point or passing point or end point of movement is used as a step of programming and, therefore, it is not possible to change contents of the program at a desired moving position during actual driving of the servo motor. When, for example, an object of control is moved by cooperation of plural shafts, these plural shafts need not always be synchronously controlled, but, in some cases, they may only need to be synchronously controlled in a desired necessary section. In such case, the prior art system is inconvenient in that contents of synchronizing or non-synchronizing program cannot be changed at desired position. Not only in such case but in others, such inconvenience tends to make the prior art system inflexible, and, therefore, improvement has been desired.